X70: UHD in firmware v3.0 compared to HD
 

Hi all,

I've just uploaded a test comparing UHD ("4K") on the X70 to HD, with firmware v3.0.

This seems of interest particularly now that we have UHD at 100Mb/second. To my eye, HD on this camera looks pretty awesome, which I have attributed to the 10-bit pixel depth; since UHD is only 8-bit, and also has a relatively low bit-rate of 100Mb/s, I was wondering how well it holds up. Of course the resolution should be a lot better.

So, I shot a bunch of test shots, including some low-light and shots with moving water for tons of motion. I've compiled these into movies that you can download and enjoy at your leisure. There are shots of the outside and inside of an old chapel; rocks on the cliffs below the chapel; and waves on rocks, with tons of motion in frame. It was dark in the chapel, but not dark enough to need gain -- both shots inside were wide open at f/2.8, zero gain.

I've posted two versions; the original files can be downloaded from these pages:

• Sony X70: UHD in v3.0 (UHD version) on Vimeo is a UHD video which contains all 6 test scenarios, with some of them having lightened versions. The HD shots have been scaled up to UHD (so of course they are less sharp).
  
• Sony X70: UHD in v3.0 (HD version) on Vimeo is a 1080p video which contains the same shots, but with the UHD shots scaled down to 1080p. I've also added some "punch-ins" on selected shots; in these the HD shot has been scaled up 200% and cropped, and the UHD shot has just been croppped. This lets people with 1080p monitors see what the UHD looks like pixel-for-pixel, when seen next to the HD.

All shots were exposed using a 95% zebra, adjusting the exposure to eliminate all zebra (except maybe in extreme hightlights). Nothing, including the exposure, was adjusted between the HD and UHD versions of shots.

Unfortunately the clouds were patchy, so the exposure did vary a little due to that, specially in the wave shots.

Also unfortunately, I screwed up on the picture profile; I didn't realise that UHD keeps its PP setting separately from HD. (And why the heck does it????) So all the HD shots were shot in PP6 as factory, and all the UHD shots were shot in PP "off". So ignore any colour shift. It doesn't seem to have hurt things too badly, as the exposures were basically the same. I'm going to re-test at least a little, to make sure that "PP off" doesn't do a ton of sharpening. (But based on the footage, I don't think so.)

My observations:

1. Framing: the UHD mode has a very slightly wider field of view -- you would think it would just be a 2:1 scaling, but apparently more is going on. The difference looks like about 6 UHD pixels horizontally.
   
2. Resolution: the UHD shots are very noticeably sharper, even when watching the HD version of the movie, even without punching in. Note that there was absolutely no change to the focus, zoom or iris -- the change of framing between the HD and UHD shots is purely coming from the camera. If you're going to deliver in HD, it looks to me like you'll get much sharper results by shooting in UHD.
   
3. Noise: both HD and UHD show noise when the exposure is raised, but it doesn't look a lot worse in UHD -- particularly look at the rocks in the middle of the last pair of shots; both show noise, but I don't think the UHD case is any worse.
   
4. Compression: I can't see any compression artifacts in the UHD (thinking about the 100 Mb/s here), even on the wave shots where there's a ton of motion in the frame, even when the brightness has been raised a lot.

(Interestingly, if I export the HD sequence at 10 Mb/s there is serious compression artifacting visible in the last shot; the UHD sequence at 40 Mb/s doesn't show it. The current exports are both 40.)

So overall I'm pleased with the UHD. I don't see the 8-bit depth being a problem, and 100 Mb/s looks like enough. What do you think?

Re: X70: UHD in firmware v3.0 compared to HD
 

Wow, I can really notice the difference in the UHD file, though it was still noticeable in the HD file too.

Thanks for sharing.

Re: X70: UHD in firmware v3.0 compared to HD
 

Atticus, I just did the 3.0 update, and I've had the UHD a long time and almost aways shoot with it. But with the 3.0 update, the dDigital extender 24x clear image zoom seems to have disappeared. The 3.0 manual does not say this, however, it mentions something in the streaming or networking, but not otherwise. Have you been able to access the Digital Extender--and if so, how?
thanks

Re: X70: UHD in firmware v3.0 compared to HD
 

It looks to me like the digital extender option is NOT there in UHD mode. The button doesn't work and the menu option is greyed out -- in HD mode, both work.

I have to ask, are you sure that the extender actually worked in UHD? It just seems logical to me that it wouldn't -- basically what it does is temporarily activate UHD, and crop the centre 1080p window out to get a zoomed-in HD picture.

If you're already shooting UHD, then that doesn't apply. It would have to capture an 8k image, and then crop out the centre 2160p window, and I just don't think the sensor can do that. I know the sensor is more than UHD, but I don't think it's that much more, or that the camera could handle that much video data, even just to crop.

Re: X70: UHD in firmware v3.0 compared to HD
 

Attitcus, since the 3.0 upgrade, and shooting in UHD, have you been able to access the D. Extender? Seems to have disappeared but the 3.0 manual doe not indicate this

Re: X70: UHD in firmware v3.0 compared to HD
 

I dont know how anybody else feels about this bit I strongly feel that shooting in UHD for 1080 delivery will create images that are far superior to ones that were shot in native 1080 for 1080 delivery. For me, the difference is striking. I really only deliver 1080 to clients but I rarely even bother shooting in 1080 anymore. I shoot, edit and master almost entirely in UHD and I just downscale a 1080 copy from the master in the end.

Plus, it can be argued that UHD 4:2:0 has enough chroma resolution to deliver a full 4:2:2 sampling equivalent in 1080 when scaled down. So, you are getting roughly 4:2:2, 1080 anyway from a 4:2:0 UHD captured image.

I have read some "experts" that SWEAR up and down that UHD 8bit color bit depth will INCREASE when you are using an NLE with a 32bit color engine during a UHD to 1080 scale down. Me?....I dont see how this is mathematically possible. I dont see how you can take pixels with 8 bit values and mix or bin them together and get anything more than just other (new) 8 bit values.

Shooting UHD for 1080 might also help with noise too. Scaling down that image in theory might scale down the "size" of the noise grit, making it look "finer" or "thinner" and possibly less noticeable.

CT

Re: X70: UHD in firmware v3.0 compared to HD
 

For every one pixel in hd you now have nearly 4 in UHD devoted to the colour information. Sure that information isn't as precise but there's still more information than there is in 4:2:0 HD - will it get rid of banding errors - no but it will reduce them.

Re: X70: UHD in firmware v3.0 compared to HD
 

Bit if you have a color graduation that ramps in 8 bit color stair steps and you take 4 different (or even similar) color pixels and average them together, you "could" easily end up with values that make banding even worse.

No matter how you average multiple 8 bit values...large numbers of 8 bit pixels or small numbers of 8 bit pixels,..., you will always end up new pixels with 8 bit color stair steps.

I dunno, if anybody can show me how to change the color bit depth from an 8 bit source into more accurate output like 10 bit, (after it was captured)...I'd love to see it.

CT